Failure Modes and Effects Analysis (FMEA) is an effective technique for identifying and eliminating possible failures. FMEA has been widely used in the manufacturing industry and in various phases of the life cycle of a product. The aim of FMEA is to ensure high quality and reliability. Design FMEA (DFMEA) is used to identify and analyze potential failure modes and their associated causes for product design. It is a verification activity that can help avoid a large percentage of product design problems before the design is finalized. When dealing with new generations of a product including design changes on the basis of existing ones, DFMEA of earlier generations can be used as a reference for such design modifications. Traditionally, criticality or risk assessment in FMEA is performed by developing a risk priority number (RPN). Failure modes that have high RPN values are assumed to be more critical and deserve more attention. In this paper, we propose a method to assess failure modes in DFMEA considering two RPNs for diesel engines. In addition to the traditional RPN, a new RPN is proposed. A diesel engine cylinder head is used as an example to illustrate the application of the two RPNs in a design FMEA.